Holographic display

RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2014-0042532, filed on Apr. 9, 2014, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field

One or more exemplary embodiments relate to a holographic display capable of displaying three-dimensional images.

2. Description of the Related Art

With the popularity of three-dimensional (3D) movies, technology for 3D image displays has been researched. 3D image displays may display 3D images based on the principal of binocular parallax or disparity. For example, binocular-parallax 3D image displays provide left-eye and right-eye images having different viewpoints to left and right eyes of viewers so that the viewers may experience a 3D effect. Such 3D image displays may be classified as glasses-type 3D image displays requiring special glasses and non-glasses-type 3D image displays not requiring special glasses.

However, viewing binocular parallax 3D images can cause eye strain. In addition, 3D image displays providing only two viewpoints, that is, left-eye and right-eye images, are not able to deal with a varying viewpoint of a moving viewer, and thus are limited in expressing 3D effects.

Therefore, holographic displays capable of providing more natural 3D images have been researched.

SUMMARY

Provided is a holographic display capable of displaying three-dimensional (3D) images.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of one or more exemplary embodiments.

According to an aspect of one or more exemplary embodiments, a holographic display includes: a light source; at least one beam steerer configured to control a propagation direction of a beam emitted from the light source; an optical element configured to condense a beam passing through the at least one beam steerer; and a spatial light modulator configured to form a three-dimensional (3D) image by modulating a beam passing through the at least one beam steerer.

The optical element includes: a collimating lens configured to collimate a beam emitted from the light source; and a field lens configured to form a viewing window of a beam passing through the spatial light modulator.

The collimating lens and the field lens are provided as a single lens.

The at least one beam steerer includes a first beam steerer and a second beam steerer disposed adjacent to each other.

The first and second beam steerers are configured to: focus a first beam emitted from the light source on a first focal point, and focus a second beam emitted from the light source on a second focal point by the first beam steerer primarily refracting the second beam and the second beam steerer secondarily refracting the second beam, thus widening a viewing angle of the holographic display.

The at least one beam steerer includes an active optical prism or a liquid crystal grating.

The at least one beam steerer includes the active optical prism. The active optical prism includes: a first electrode; a second electrode disposed facing the first electrode; a first medium disposed between the first and second electrodes; and a second medium disposed between the first and second electrodes, the first and second media having different refractive indexes.

The first medium includes a nonpolar fluid, and the second medium includes a polar fluid.

The first medium includes oil, and the second medium includes water.

The optical element includes a wave guide disposed between the at least one beam steerer and the spatial light modulator.

The at least one beam steerer is further configured to control the propagation direction of a light emitted from the light source to mimic light emitted from at least one virtual light source, the light mimicking being emitted from the at least one virtual light source being focused on a virtual focal point.

Light emitted from the light source without being controlled to mimic light emitted from a virtual light source is focused on a focal point. The holographic display satisfies the following equation: &lt;br /&gt;<i>A/B=A′/B′</i>

where A denotes a distance between the light source and the spatial light modulator, B denotes a distance between the spatial light modulator and the focal point, A′ denotes a distance between the light source and the at least one virtual light source, and B′ denotes a distance between the focal point and the virtual focal point.

The at least one beam steerer is disposed closer to the light source than the spatial light modulator.

D is a distance between the light source and the spatial light modulator, and the at least one beam steerer is disposed within a range of D/2 from the light source.

The at least one beam steerer is further configured to focus a plurality of beams emitted from the light source on a plurality of focal points.

The light source is configured to emit coherent light.

The at least one beam steerer includes an active optical prism comprising a plurality of prism units. The plurality of prism units include respective: first electrodes; second electrodes disposed facing the first electrode; first media disposed between the first and second electrodes; and second media disposed between the first and second electrodes, the first and second media having different refractive indexes.

The at least one beam steerer comprises a liquid crystal grating includes: a first glass substrate; a second glass substrate; a first electrode disposed on the first glass substrate; a second electrode disposed on the second glass substrate; and a refractive index change layer disposed between the first and second glass substrates, the refractive index change layer including a plurality of liquid crystals and a plurality of prisms arranged in an alternating pattern.

The optical element includes a wave guide configured to guide a beam passing through the at least one beam steerer. The spatial light modulator is disposed in a direction different from a straight light propagation direction of the light source and the at least one beam steerer.

The at least one beam steerer is disposed between the optical element and the light source, the collimating lens is disposed between the at least one beam steerer and the spatial light modulator, and the spatial light modulator is disposed between the collimating lens and the field lens.

According to an aspect of one or more exemplary embodiments, a holographic display includes: a light source; a beam steerer configured to control a propagation direction of light emitted from the light source; a collimating lens configured to collimate light that exits the beam steerer; a spatial light modulator configured to form a three-dimensional (3D) image by modulating the collimated light; and a field lens configured to form a viewing window of the light that exits the spatial light modulator.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readily appreciated from the following description of one or more embodiments, taken in conjunction with the accompanying drawings in which:

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view illustrating a holographic display according to an exemplary embodiment;

<figref idref="DRAWINGS">FIGS. 2 to 4</figref> are views illustrating a beam steering element of the holographic display according to one or more exemplary embodiments;

<figref idref="DRAWINGS">FIG. 5</figref> is a view illustrating a beam steering element of the holographic display according to an exemplary embodiment;

<figref idref="DRAWINGS">FIG. 6</figref> is a view illustrating a beam steering element of the holographic display according to an exemplary embodiment;

<figref idref="DRAWINGS">FIG. 7</figref> is a schematic view illustrating a holographic display according to an exemplary embodiment; and

<figref idref="DRAWINGS">FIG. 8</figref> is a schematic view illustrating a holographic display according to another embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to one or more exemplary embodiments, examples of which are illustrated in the accompanying drawings. In this regard, one or more exemplary embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the exemplary embodiments described below, by referring to the figures, explain various aspects of one or more exemplary embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

Hereinafter, a holographic display will be described in detail according to one or more exemplary embodiments with reference to the accompanying drawings. In the drawings, like reference numbers refer to like elements, and the sizes of elements may be exaggerated for clarity of illustration. The exemplary embodiments described herein are for illustrative purposes only, and various modifications may be made thereto. It will also be understood that when a layer is referred to as being “on top of,” “above,” or “on” another layer or substrate, it can be directly on top of, above, or on the other layer or substrate, or intervening layers may also be present, unless explicitly described otherwise.

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view illustrating a holographic display <b>1</b> according to an exemplary embodiment. The holographic display <b>1</b> includes a light source <b>10</b>, at least one beam steering element <b>90</b>, i.e., at least one beam steerer, configured to control the direction of a beam emitted from the light source <b>10</b>, an optical element <b>70</b> configured to condense a beam passing through the beam steering element <b>90</b>, and a spatial light modulator <b>50</b> configured to modulate a beam passing through the at least one beam steering element <b>90</b> to form a 3D image.

The holographic display <b>1</b> is operated using wave properties of light such as diffraction or interference. However, autostereoscopic displays, multi-view displays, or super multi-view displays are operated using particle characteristics of light. Displays using wave characteristics of light and displays using particle properties of light are conceptually different displays.

The light source <b>10</b> may emit coherent light. Coherent light may have a constant wavelength and be collimated. For example, the light source <b>10</b> may include a laser unit, a light emitting device (LED), or a laser diode (LD). However, the light source <b>10</b> is not limited thereto.

The at least one beam steering element <b>90</b> may include a first beam steering element <b>20</b>, i.e., a first beam steerer, and a second beam steering element <b>30</b>, i.e., a second beam steerer. The first and second beam steering elements <b>20</b> and <b>30</b> may be disposed adjacent to each other. The first and second beam steering elements <b>20</b> and <b>30</b> may be adjacent to each other without any element disposed therebetween. The at least one beam steering element may be bigger or smaller than the spatial light modulator <b>50</b>. The at least one beam steering element <b>90</b> may be disposed between the light source <b>10</b> and the spatial light modulator <b>50</b>. The at least one beam steering element <b>90</b> may be closer to the light source <b>10</b> than the spatial light modulator <b>50</b>. That is, the distance A<b>1</b> between the at least one beam steering element <b>90</b> and the light source <b>10</b> may be shorter than the distance A<b>2</b> between the at least one beam steering element <b>90</b> and the spatial light modulator <b>50</b>. In this case, the distances A<b>1</b> and A<b>2</b> may be measured based on a beam steering element of the at least one beam steering element <b>90</b> relatively distant from the light source <b>10</b>. For example, the distance A<b>1</b> between the light source <b>10</b> and the second beam steering element <b>30</b> may be shorter than the distance A<b>2</b> between the second beam steering element <b>30</b> and the spatial light modulator <b>50</b>. For example, the at least one beam steering element <b>90</b> may be disposed within a range from the light source <b>10</b> that is half the distance (A) between the light source <b>10</b> and the spatial light modulator <b>50</b>. If the at least one beam steering element <b>90</b> is disposed close to the light source <b>10</b>, the size of the at least one beam steering element <b>90</b> may be decreased. That is, if the at least one beam steering element <b>90</b> is disposed close to the light source <b>10</b>, a region of the at least one beam steering element <b>90</b> onto which light emitted from the light source <b>10</b> is incident may be decreased, and thus the size of the at least one beam steering element <b>90</b> may be decreased. The at least one beam steering element <b>90</b> may be smaller than the spatial light modulator <b>50</b>. If the size of the at least one beam steering element <b>90</b> is decreased, the size of the holographic display <b>1</b> may also be decreased.

The at least one beam steering element <b>90</b> may control the direction of a beam emitted from the light source <b>10</b>. The at least one beam steering element <b>90</b> may include at least one selected from the group consisting of diffraction devices, refraction devices, and reflection devices. For example, the at least one beam steering element <b>90</b> may include at least one selected from the group consisting of active optical prisms, liquid crystal gratings, and variable mirrors.

The optical element <b>70</b> may condense a beam passing through the at least one beam steering element <b>90</b>. For example, the optical element <b>70</b> may include a collimating lens <b>40</b> configured to collimate a beam passing through the at least one beam steering element <b>90</b>, and a field lens <b>60</b> configured to adjust a beam passing through the spatial light modulator <b>50</b> for obtaining a desired viewing window (viewing angle). The field lens <b>60</b> may be a condensing lens, and light diverging from the light source <b>10</b> may be condensed on the viewing window by the field lens <b>60</b>. For example, the field lens <b>60</b> may be a diffractive optical element or a holographic optical element manufactured by forming the phase of a lens on a flat surface. The collimating lens <b>40</b> may be disposed in front of the spatial light modulator <b>50</b>, and the field lens <b>60</b> may be disposed behind the spatial light modulator <b>50</b>. However, one or more exemplary embodiments are not limited thereto. For example, the collimating lens <b>40</b> and the field lens <b>60</b> may be disposed behind the spatial light modulator <b>50</b>.

The spatial light modulator <b>50</b> may receive an image signal and may modulate at least one of an amplitude and a phase of a beam emitted from the light source <b>10</b> according to the image signal. A beam modulated by the spatial light modulator <b>50</b> may form 3D images. For example, the spatial light modulator <b>50</b> may include an optical electrical device having refractive index variable according to an electric signal. For example, the spatial light modulator <b>50</b> may include an optical electrical material layer such as a liquid crystal layer. The phase of light passing through the spatial light modulator <b>50</b> may be controlled by applying a voltage to the optical electrical material layer to vary the refractive index of the optical electrical material layer. For example, the spatial light modulator <b>50</b> may include a computer generated hologram (CGH). The spatial light modulator <b>50</b> may include a plurality of pixels. The plurality of pixels of the spatial light modulator <b>50</b> may be arranged in the form of a two-dimensional matrix.

Next, an explanation will be given of how the holographic display <b>1</b> of one or more exemplary embodiments is operated.

A beam may be emitted from the light source <b>10</b>, and the propagation direction of the beam may be changed by the at least one beam steering element <b>90</b>. The at least one beam steering element <b>90</b> may create at least one virtual light source <b>10</b><i>a</i>. For example, the at least one beam steering element <b>90</b> may change the propagation direction of light emitted from the light source <b>10</b> to create an effect that a beam is emitted from a different position (i.e., the virtual light source <b>10</b><i>a</i>) from the light source <b>10</b>.

For example, a first beam L<b>1</b> emitted from the light source <b>10</b> may pass through the first and second beam steering elements <b>20</b> and <b>30</b>, the collimating lens <b>40</b>, the spatial light modulator <b>50</b>, and the field lens <b>60</b>, and may then be focused on a first focal point P<b>1</b>. If the propagation direction of a second beam L<b>2</b> emitted from the light source <b>10</b> is varied by the first and second beam steering elements <b>20</b> and <b>30</b>, the effect that the second beam L<b>2</b> emitted from the virtual light source <b>10</b><i>a </i>adjacent to the light source <b>10</b> is focused on a virtual second focal point P<b>2</b> may be obtained. That is, the second beam L<b>2</b> emitted from the virtual light source <b>10</b><i>a </i>may be focused on the virtual second focal point P<b>2</b>.

Although a single virtual light source (the virtual light source <b>10</b><i>a</i>) is described as an example, in one or more exemplary embodiments, two or more virtual light sources may be created corresponding to two or more virtual focal points.

The light source <b>10</b> and the virtual light source <b>10</b><i>a </i>may satisfy the following Expression 1: &lt;br /&gt;<i>A/B=A′/B′</i>  &lt;Expression 1&gt;

where A denotes a distance between the light source <b>10</b> and the spatial light modulator <b>50</b>, B denotes a distance between the spatial light modulator <b>50</b> and the first focal point P<b>1</b>, A′ denotes a distance between the light source <b>10</b> and the virtual light source <b>10</b><i>a</i>, and B′ denotes a distance between the first focal point P<b>1</b> and the virtual second focal point P<b>2</b>. If Expression 1 is satisfied, a beam emitted from the virtual light source <b>10</b><i>a </i>may be focused on an imaging plane.

The first and second beam steering elements <b>20</b> and <b>30</b> may control the propagation direction of a beam to satisfy Expression 1. For example, a first beam L<b>1</b> may pass through the first beam steering element <b>20</b> and the second beam steering element <b>30</b> and may focus on the first focal point P<b>1</b>. A second beam L<b>2</b> may be primary refracted by the first beam steering element <b>20</b> and secondarily refracted by the second beam steering element <b>30</b>, thereby obtaining the effect that the second beam L<b>2</b> is emitted from the virtual light source <b>10</b><i>a </i>adjacent to the light source <b>10</b> and is focused on the virtual second focal point P<b>2</b>. In this manner, the viewing angle of the holographic display <b>1</b> may be increased using the first and second beam steering elements <b>20</b> and <b>30</b>.

The viewing angle of the holographic display <b>1</b> may be determined according to the degree of diffraction and spreading of light. The following expression 2 relates to a diffraction angle. &lt;br /&gt;Sin(θ/2)=λ/<i>d</i>  &lt;Expression 2&gt;

where θ denotes the angle of diffraction, λ denotes the wavelength of light, and d denotes a pixel size. According to Expression 2, the degree of light spreading (diffraction angle) may depend on the wavelength of light and the pixel size. That is, the viewing angle of the holographic display <b>1</b> may be determined by the pixel size. For example, the pixel size may be required to decrease to 1 μm or less for obtaining a sufficient viewing angle. However, it is difficult to manufacture the holographic display <b>1</b> if the pixel size of the holographic display <b>1</b> is too small. According to one or more exemplary embodiments, the viewing angle of the holographic display <b>1</b> may be increased by using the beam steering element <b>90</b> without having to increase the pixel size of the holographic display <b>1</b>. In the holographic display <b>1</b>, a plurality of pixels may be simultaneously used to express a single point in a space, and a plurality of spatial points may be expressed using a single pixel.

For example, the at least one beam steering element <b>90</b> may be an active optical prism. <figref idref="DRAWINGS">FIG. 2</figref> illustrates an exemplary active optical prism <b>150</b>.

Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the active optical prism <b>150</b> may be divided into a plurality of prism units <b>152</b>, and the slopes of refraction surfaces <b>154</b> of the prism units <b>152</b> may be adjusted according to an electric signal so as to control the exit angles of light passing through the prism units <b>152</b>. The active optical prism <b>150</b> may include an electric wetting device. The prism units <b>152</b> may be partitioned by barrier walls <b>156</b>, and each of the prism units <b>152</b> may include a prism <b>155</b>.

The prism units <b>152</b> of the active optical prism <b>150</b> may be two-dimensionally arranged.

<figref idref="DRAWINGS">FIG. 3</figref> is a schematic view illustrating a prism unit <b>152</b> of the active optical prism <b>150</b> according to an exemplary embodiment. Referring to <figref idref="DRAWINGS">FIG. 3</figref>, the prism unit <b>152</b> may include a first electrode <b>162</b><i>a </i>and a second electrode <b>162</b><i>b </i>that face each other. A first medium <b>165</b> and a second medium <b>166</b> having different refractive indexes may be disposed between the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>. For example, the first medium <b>165</b> may be a nonpolar fluid, and the second medium <b>166</b> may be a polar fluid. For example, the first medium <b>165</b> may be oil, and the second medium <b>166</b> may be water, alcohol, glycerin, or salt water. An interface between the first medium <b>165</b> and the second medium <b>166</b> functions as the refraction surface <b>154</b>. Hydrophobic films <b>164</b> may be disposed on inner sides of the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>, respectively. In addition, an insulation layer <b>163</b> may be disposed between the first electrode <b>162</b><i>a </i>and the hydrophobic film <b>164</b>, and another insulation layer <b>163</b> may be disposed between the second electrode <b>162</b><i>b </i>and the hydrophobic film <b>164</b>. The insulation layers <b>163</b> may be formed of a hydrophobic material. In this case, the hydrophobic films <b>164</b> are not used.

In one or more exemplary embodiments, the prism unit <b>152</b> is operated by the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>. However, one or more exemplary embodiments are not limited thereto. For example, the prism unit <b>152</b> may be operated by four electrodes disposed on four lateral sides thereof.

If a voltage is not applied between the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>, the first medium <b>165</b> forms a large contact angle θ with the hydrophobic film <b>164</b>. If a voltage is applied between the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>, the contact angle θ between the hydrophobic film <b>164</b> and the first medium <b>165</b> is decreased, and the slope of the refraction surface <b>154</b> is varied. If the slope of the refraction surface <b>154</b> of the prism unit <b>152</b> is varied, the exit direction (propagation direction) of light passing through the prism unit <b>152</b> is varied. In this way, the propagation direction of light may be controlled by applying a voltage between the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b </i>in an on-off manner or by varying a voltage applied between the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>. In <figref idref="DRAWINGS">FIG. 3</figref>, light L is refracted by the refraction surface <b>154</b> toward a left side. <figref idref="DRAWINGS">FIG. 4</figref> illustrates that the refraction surface <b>154</b> is adjusted to be parallel with a light entrance surface by applying a voltage between the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>. In this case, light L may pass through the refraction surface <b>154</b> at a right angle. The slope of the refraction surface <b>154</b> may be varied according to the magnitude and direction of a voltage applied between the first and second electrodes <b>162</b><i>a </i>and <b>162</b><i>b</i>, and the propagation direction of light may be varied according to the slope of the refraction surface <b>154</b>.

In one or more exemplary embodiments, the propagation direction of light may be adjusted using the active optical prism <b>150</b> so as to increase the angle of propagation light, and thus increase the viewing angle of the holographic display <b>1</b>.

<figref idref="DRAWINGS">FIG. 5</figref> is a schematic view illustrating a liquid crystal grating <b>170</b> as the beam steering element <b>190</b> according to an exemplary embodiment.

The liquid crystal grating <b>170</b> may include a first glass substrate <b>171</b>, a second glass substrate <b>172</b>, and a liquid crystal layer <b>173</b> disposed between the first and second glass substrates <b>171</b> and <b>172</b>. A first electrode <b>174</b> may be provided on a side of the first glass substrate <b>171</b>, and a second electrode <b>175</b> may be provided on a side of the second glass substrate <b>172</b>. The first and second electrodes <b>174</b> and <b>175</b> may be transparent electrodes.

At least one of the first electrode <b>174</b> and the second electrode <b>175</b> may include unit electrodes formed by patterning, and voltages may be independently applied to the unit electrodes. For example, the first electrode <b>174</b> may include first to sixth unit electrodes <b>174</b><i>a</i>, <b>174</b><i>b</i>, <b>174</b><i>c</i>, <b>174</b><i>d</i>, <b>174</b><i>e</i>, and <b>174</b><i>f</i>. A first voltage V<b>1</b>, a second voltage V<b>2</b>, a third voltage V<b>3</b>, and a fourth voltage V<b>4</b>, may be applied to the first unit electrode <b>174</b><i>a</i>, the second unit electrode <b>174</b><i>b</i>, the third unit electrode <b>174</b><i>c</i>, and the fourth unit electrode <b>174</b><i>d</i>, respectively. The first to fourth voltages V<b>1</b>, V<b>2</b>, V<b>3</b>, and V<b>4</b> may satisfy the inequality of V<b>1</b>&lt;V<b>2</b>&lt;V<b>3</b>&lt;V<b>4</b>. The first voltage V<b>1</b> and the second voltage V<b>2</b> may also be applied to the fifth unit electrode <b>174</b><i>e </i>and the sixth unit electrode <b>174</b><i>f</i>, respectively.

The refractive index of the liquid crystal layer <b>173</b> may be varied according to voltages applied between the first and second electrodes <b>174</b> and <b>175</b>. For example, if voltages are sequentially or simultaneously applied to a pattern of the second electrode <b>175</b>, the liquid crystal layer <b>173</b> may function as a prism or blazed grating in response to the applied voltages. The optical path of light may be varied by adjusting the magnitudes and order of voltages applied to each electrode pattern so as to operate the liquid crystal layer <b>173</b> as a prism or blazed grating.

Next, <figref idref="DRAWINGS">FIG. 6</figref> illustrates a liquid crystal grating <b>180</b> according to an exemplary embodiment.

The liquid crystal grating <b>180</b> may include a first glass substrate <b>181</b>, a second glass substrate <b>182</b>, and a refractive index change layer <b>183</b> disposed between the first and second glass substrates <b>181</b> and <b>182</b>. A first electrode <b>184</b> may be provided on a side of the first glass substrate <b>181</b>, and a second electrode <b>185</b> may be provided on a side of the second glass substrate <b>182</b>. The first and second electrodes <b>184</b> and <b>185</b> may be transparent electrodes. The refractive index change layer <b>183</b> may have a structure in which liquid crystal parts <b>186</b> and prisms <b>187</b> are alternatively arranged.

The refractive indexes of the liquid crystal parts <b>186</b> may be varied according to voltage applied between the first and second electrodes <b>184</b> and <b>185</b>. When the refractive indexes of the liquid crystal parts <b>186</b> are equal to the refractive indexes of the prisms <b>187</b>, light may propagate straight through the index change layer <b>183</b>. When the refractive indexes of the liquid crystal parts <b>186</b> are different from the refractive indexes of the prisms <b>187</b>, light may be refracted. That is, the propagation direction of light may be varied.

<figref idref="DRAWINGS">FIG. 7</figref> is a schematic view illustrating a modified holographic display according to an exemplary embodiment. In the example illustrated in <figref idref="DRAWINGS">FIG. 1</figref>, the optical element <b>70</b> includes the collimating lens <b>40</b> and the field lens <b>60</b>. However, in the example illustrated in <figref idref="DRAWINGS">FIG. 7</figref>, a collimating lens and a field lens are combined into a single optical element <b>55</b>. Since the optical element <b>55</b> has a combined structure, the holographic display may have a smaller size. The optical element <b>55</b> may be disposed in front of a spatial light modulator <b>50</b>.

The other elements illustrated in <figref idref="DRAWINGS">FIG. 7</figref> are substantially similar to those illustrated in <figref idref="DRAWINGS">FIG. 1</figref>, and thus detailed descriptions thereof will not be repeated.

<figref idref="DRAWINGS">FIG. 8</figref> is a schematic view illustrating a holographic display <b>200</b> according to another exemplary embodiment. The holographic display <b>200</b> includes a light source <b>210</b>, at least one beam steering element <b>290</b> configured to control the direction of a beam emitted from the light source <b>210</b>, an optical element <b>240</b> configured to condense a beam passing through the at least one beam steering element <b>290</b>, and a spatial light modulator <b>250</b> configured to modulate a beam passing through the at least one beam steering element <b>290</b> so as to form a 3D image.

The at least one beam steering element <b>290</b> may include a first beam steering element <b>220</b> and a second beam steering element <b>230</b>. The first and second beam steering elements <b>220</b> and <b>230</b> may be disposed adjacent to each other. The first and second beam steering elements <b>220</b> and <b>230</b> may be disposed between the light source <b>210</b> and the optical element <b>240</b>. For example, the first and second beam steering elements <b>220</b> and <b>230</b> may be disposed within a range of less than half the distance D between the light source <b>210</b> and the spatial light modulator <b>250</b>. The distance D between the light source <b>210</b> and the spatial light modulator <b>250</b> may be an optical distance.

The optical element <b>240</b> may be a wave guide configured to guide a beam passing through the second beam steering element <b>230</b>. The spatial light modulator <b>250</b> may display 3D images using a beam coming from the optical element <b>240</b>. The structure of the holographic display <b>200</b> may be changed owing to the optical element <b>240</b> varying the propagation direction of light. In other words, elements of the holographic display <b>200</b> may be arranged in a direction different from a straight light propagation direction, and thus the holographic display <b>200</b> may have an efficient element arrangement.

The first and second beam steering elements <b>220</b> and <b>230</b> may include an active optical prism or a liquid crystal grating. The first and second beam steering elements <b>220</b> and <b>230</b> may control the propagation direction of a beam.

The at least one beam steering element <b>290</b> may create at least one virtual light source <b>210</b><i>a</i>. The at least one beam steering element <b>290</b> may change the propagation direction of light emitted from the light source <b>210</b> to create an effect that a beam is emitted from a different position (i.e., the virtual light source <b>210</b><i>a</i>) from the light source <b>210</b>.

For example, a first beam L<b>1</b> emitted from the light source <b>210</b> may pass through the first and second beam steering elements <b>220</b> and <b>230</b>, the optical element <b>240</b>, and the spatial light modulator <b>250</b>, and may then be focused on a first focal point P<b>1</b>. If the propagation direction of a second beam L<b>2</b> emitted from the light source <b>210</b> is varied by the first and second beam steering elements <b>220</b> and <b>230</b>, the second beam L<b>2</b> may appear to be emitted from the virtual light source <b>210</b><i>a </i>and be focused on the second focal point P<b>2</b>. For example, the second beam L<b>2</b> may be primarily refracted by the first beam steering element <b>220</b> and secondarily refracted by the second beam steering element <b>230</b>, thereby obtaining the effect that the second beam L<b>2</b> is emitted from the virtual light source <b>210</b><i>a </i>and focused on the second focal point P<b>2</b>. In <figref idref="DRAWINGS">FIG. 8</figref>, a single virtual light source (the virtual light source <b>210</b><i>a</i>) is described. However, two or more virtual light sources may be created by the first and second beam steering elements <b>220</b> and <b>230</b>.

As described above, according to the one or more of the above exemplary embodiments, the holographic display may control a region in which images are formed so as to provide a wide image display region.

It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments.

While one or more exemplary embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents.